Cryogenic cooling apparatus and method

Abstract

A method is provided of operating a cryogenic cooling system, in which a target region for receiving a sample is cooled by a dilution refrigerator containing an operational fluid. Firstly any operational fluid is removed from the dilution refrigerator. Target apparatus comprising the sample is loaded from a high temperature location to the target region. The target apparatus is then pre-cooled in the target region to a first temperature using a mechanical refrigerator. The operational fluid is then supplied to the dilution refrigerator and the dilution refrigerator operated so as to cool the target apparatus in the target location to a second temperature that is lower than the first temperature. A suitable system for performing the method is also disclosed.

The invention claimed is: 
     
       1. A method of operating a cryogenic cooling system, in which a target region for receiving a sample is cooled by a dilution refrigerator containing an operational fluid, the method comprising performing the following steps (a)-(e) in order:
 a) removing the operational fluid from the dilution refrigerator; 
 b) moving target apparatus comprising the sample from a high temperature location to the target region; 
 c) pre-cooling the apparatus in the target region to a first temperature using a mechanical refrigerator; 
 d) providing the operational fluid to the dilution refrigerator; and 
 e) operating the dilution refrigerator using the operational fluid so as to cool the target apparatus in the target location to a second temperature that is lower than the first temperature. 
 
     
     
       2. A method according to  claim 1 , wherein the target region is at a lower temperature than the high temperature location during step (b). 
     
     
       3. A method according to  claim 2 , wherein said lower temperature is below 30 kelvin and wherein thermal contact of the target apparatus with the target region during step (b) causes a heat transfer from the target apparatus to the target region. 
     
     
       4. A method according to  claim 1 , wherein the target region remains at a temperature below 100 kelvin during steps(a)-(e). 
     
     
       5. A method according to  claim 1 , wherein the cryogenic cooling system comprises a cryostat having an interior volume which is in an evacuated state during steps (a)-(e). 
     
     
       6. A method according to  claim 1 , wherein step (a) comprises heating the operational fluid so as to cause it to become fully gaseous, and removing the operational fluid to external location. 
     
     
       7. A method according to  claim 1 , wherein step (b) comprises only performing a cooling operation upon the target apparatus once the target apparatus is positioned within the target region. 
     
     
       8. A method according to  claim 1 , wherein the positioning of the target apparatus in the target region comprises attaching the target apparatus to a thermally conductive member so as to provide thermally conductive cooling of the target apparatus using the conductive member. 
     
     
       9. A method according to  claim 1 , wherein step (c) comprises causing coolant to flow within a pre-cooling circuit located in thermal contact with the mechanical refrigerator and the target region. 
     
     
       10. A method according to  claim 9  wherein the coolant in the pre-cooling circuit and the operational fluid are the same coolant. 
     
     
       11. A method according to  claim 9 , where, following step (c) the coolant is removed from the pre-cooling circuit. 
     
     
       12. A method according to  claim 9 , further comprising, during step (a), providing coolant at a high temperature into the pre-cooling circuit so as to heat the target region. 
     
     
       13. A method according to  claim 1 , wherein the high temperature location is positioned within an ambient environment. 
     
     
       14. A method according to  claim 1  wherein, prior to step (a), the dilution refrigerator is at a temperature such that part of the operational fluid is liquid. 
     
     
       15. A method according to  claim 1 , wherein, prior to step (d) the temperature of the dilution refrigerator is less than about 10 kelvin. 
     
     
       16. A method according to  claim 1 , wherein in step (b) the target apparatus is moved to the target location whilst the target apparatus is attached to a loading assembly and wherein, once in the target region, the target apparatus is released from the loading assembly and the loading assembly is retracted. 
     
     
       17. A method according to  claim 1 , wherein steps (a) and steps (c) to (e) are performed automatically under the control of a control system. 
     
     
       18. A cryogenic cooling system comprising:
 a dilution refrigerator arranged to use operational fluid to cool a target region at which target apparatus, comprising a sample, is positioned when in use; 
 a pre-cool system, comprising a mechanical refrigerator, for cooling the target apparatus in the target region; and, 
 a control system adapted when in use to remove the operational fluid from the dilution refrigerator before the target apparatus is received at the target region, to operate the pre-cool system so as to pre-cool the target apparatus in the target region to a first temperature using the mechanical refrigerator, to provide the operational fluid to the dilution refrigerator and to operate the dilution refrigerator using the operational fluid so as to cool the target apparatus in the target location to a second temperature that is lower than the first temperature. 
 
     
     
       19. A cryogenic system according to  claim 18 , wherein the mechanical refrigerator comprises any of: a Gifford-McMahon cooler, a Stirling cooler or a pulse tube refrigerator. 
     
     
       20. A cryogenic system according to  claim 18 , further comprising a storage vessel for storing operational coolant, the storage vessel being selectively connectable to the dilution refrigerator. 
     
     
       21. A system according to  claim 18 , wherein the pre-cool system comprises a pre-cooling circuit arranged to supply a cooling fluid between the mechanical refrigerator and the target apparatus at the target region. 
     
     
       22. A cryogenic system according to  claim 21 , wherein the storage vessel is selectively connectable to the pre-cool system and wherein the cooling fluid is the operational fluid. 
     
     
       23. A cryogenic system according to  claim 18 , wherein the operational fluid is a mixture of helium-3 and helium-4. 
     
     
       24. A cryogenic system according to  claim 18 , further comprising a plurality of spatially disposed stages to which parts of the mechanical and dilution refrigerators are coupled. 
     
     
       25. A cryogenic system according to  claim 24 , wherein one or more of the plurality of stages has an aperture for receiving the target apparatus and wherein the said one or more apertures defines a bore through which the target apparatus is caused to pass. 
     
     
       26. A cryogenic system according to  claim 25 , wherein at least one of the apertures is provided with a baffle which is moveable between an open position in which the aperture is accessible and a closed position in which the aperture is closed. 
     
     
       27. A cryogenic system according to  claim 18 , further comprising one or each of electrical and optical communication lines for communicating with the sample, the said lines being fixed within the apparatus, independently of the presence or absence of the target apparatus and the said lines being provided from an external location to the target region. 
     
     
       28. A cryogenic system according to  claim 27 , wherein the communication lines do not pass through any of the said one or more apertures. 
     
     
       29. A cryogenic system according to  claim 18 , wherein the cryogenic system comprises a cryogen-free system. 
     
     
       30. A non-transitory computer readable medium storing a program causing a controller to perform the steps (a) and (c) to (e) of the method of  claim 1  in order.